Azo pigments and coating compositions containing same



Pmmd May 23, 1950 AZO PIGMENTS AND COATING COMPOSI- TIONS CONTAININGSAME Alfred Anthony Brizzolara, Bellevllle, N. J., as-

signor to E. I. du Pont de Nemours & Company, Wilmington, Del., acorporation of Delaware No Drawing. Application February 3, 1948, SerialNo. 6,021

6 Claims.

This invention relates to improved maroon coating compositions, and moreparticularly to maroon enamels of excellent durability and relativefreedom from reactivity on storage, and to pigment compositions forobtaining such coating compositions.

In the copending application for United States Letters Patent of JosephH. Cooper, Serial No. 648,835, filed February 19, 1946, a novel maroonazo pigment and method for producing the same is disclosed. Such pigmentis obtained by coupling diazotized -nitro-2-amino anisole with the orthotoluidide of 2-hydroxy-3-naphthoic acid, and is represented by theformula As therein disclosed, maroon'enamels containing such pigmentexhibit a degree of durability not heretofore obtainable in similarvehicles with known pigments of comparable color. Due to itsexceptionally good durability characteristics in both nitrocelluloselacquer and alkyd resin enamels, its combination of dark masstone withyellow undertone and relatively high transparency, such pigment iseminently suited for use in automotive finishes.

Despite the superior properties of the enamel films made with the abovepigment, such enamels exhibit certain defects which disadvantageouslyreduce their usefulness. These defects manifest themselves in a serioustendency of the enamels to become progressively more viscous on storagewhereby eventually they become gell-like in form and hence no longerutilizable in their intended purpose. This phenomenon is generallyattributed to reactivity of the pigment with the coating compositionvehicle in which the pigment is dispersed.

Thus, if enamels such as those described in said copending Cooperapplication Serial No. 648,835 are used immediately after grinding, thebenefits ascribed to the use of the new maroon pigment are readilyattained. If, however, such the enamel can no longer be employed in theuse intended.

It has now been found that the disadvantageous characteristics exhibitedin enamel coatings by an insoluble maroon azo pigment of the typementioned in the aforesaid sZooper application can be efiectivelyremedied, and, accordingly, it

' is among the'objects of this invention to prepare enamels are storedfor substantial periods of time,

in most instances they will be found to be much more viscous thanoriginally and, in many cases, depending on the length of time ofstorage or an improved form of pigment composition for use in suchcoatings, as well as to prepare maroon synthetic enamels of desirabledurability and which are relatively free from objectionable reactivityand resistant toward becoming more viscous on storage. A further objectis to provide for the preparation of new maroon pigmentcompositionswhich do not induce objectionable reactivity in syntheticenamel vehicles. other objects and advantages of the invention will beevident from the ensuing description thereof.

These and other objects are attained in this invention which comprisesemploying in a coating composition susceptible to reactivity in thepresence of the pigment composition set forth in said Cooper applicationSerial No. 648,835, a regulated proportion of an additional azopigmenting substance, viz., a metal salt of the azo dyestufi obtained bycoupling 5-nitro-2-amino anisole with 2-hydroxy-3-naphthoic acid.

In a more specific and preferred embodiment, the invention comprisesutilizing as an essential pigmenting ingredient in a maroon syntheticenamel, in order to impart improved durability and stabilitycharacteristics thereto, a pigment mixture comprising a major amount(about to of the total pigment composition) of the azo pigment resultingfrom coupling diazotized 5-nitro-2-amino anisole with the orthotoluidide of 2-hydroxy-3-naphthoic acid, and a minor amount (about 25%to 5% of the total pigment present) of the manganese salt of the azodyestufi resulting from coupling diazotized 5-nitro-2- amino anisolewith 2-hydroxy-3-naphthoicacid.

In practically applying the invention, two steps are involved. In thefirst step, the adjuvant pigment mixture is prepared in the desiredform, while in the second step a desired coating composition utilizingsuch pigment in the proper amount is prepared.

The accomplishment of the first step involves the preparation andadmixture of the pigmenting ingredients or complex which is to beemployed in the coating formulation. Thus, diazotization can beconveniently effected of 5-nitro-2-amino anisole by conventional meanswith coupling of standing, will have proceeded to the point where 52-hydroxy-3-na'phthoic acid preferably in a suspension buffered withsodium bicarbonatebeing then had. The pigment can then be isolated andused in the form of its free acid or sodium salt but since it contains asolubilizing carboxy group, it is preferred to convert it to aninsoluble metallic salt of which the manganese salt is most desirableand preferred. Complete conversion to the insoluble manganese (or othermetal) salt requires some heat development. It has been found that twoforms of the pigment can be obtained, that these two forms exhibitdifferent X-ray diffraction patterns, presumably because of uniquecrystal structures, that they exhibit widely different tinctorialproperties and that they differ widely in their degree of effectivenessfor the purposes of this invention.

Thus, if the pigment slurry coupled by the preferred method is rapidlyheated in the presence of a solution of a manganese salt to the boil andthen quickly cooled, the preferred form of the igment is obtained. Itexhibits a dark maroon masstone and a relatively weak bluish tint. If,on the other hand, the heat development is continued for a longerperiod, the masstone becomes much lighter and the tint much stronger andyellower. Although in many ways more desirable as a pigment, this secondform, though contemplated as utilizable herein, is less effective foruse in the invention.

Similarly, diazotization and coupling of 5- nitro-Z-amino anisole withthe ortho toluidide of beta-hydroxy naphthoic acid is effected inaccordance with the disclosure of said Cooper application Ser. No.648,835. The resulting pigments are then intimately associated with oneanother in a conventional paddle type or other form Of mechanical mixer,preferably in the percentage proportions set out above.

Following preparation of my novel pigment complex, I then resort to thesecond or final step of my invention, i. e., the pigment mixture is,dis-'persed in a suitable coating composition, preferably an enamel vehicle,by grinding in a suitable paint or other conventional mechanical mill.

To a clearer understanding of the invention, the following specific andillustrative examples are given:

EXAMPLE I An adjuvant pigment useful in the invention was prepared byfirst slurrying 204 lbs. of 5-nitro- 2-amino anisole in 248 gallons ofwater. To the resulting slurry a solution of hydrochloric acidequivalent to 129 lbs. of 100% HCl was added. After stirring a fewminutes the suspension was cooled with ice to 0 C. at a volume of about500 gallons and a solution of 84 lbs. sodium nitrite in about 100gallons water was added over a a about by adding the diazo beneath thesurface of the well-agitated suspension over a period of to minutes.After a short stirring period to insure completion of coupling, asolution of 272 lbs. of manganese sulfate in a total volume of about 360gallons was added slowly and the pigment suspension heated rapidly tothe boil and immediately filtered, washed free of soluble chlorides anddried at a temperature of about 60 C. About 504 lbs. of a dark maroonpigment resulted.

Ten pounds of the maroon pigment thus obtained were then thoroughlymixed in a conventional paddle mixer with 901128. of the maroon pigmentobtained by couplingdiazotized 5-nitro- 2-amino anisole with the orthotoluidide of 2- hydroxy-3-naphthoic acid, as described in said Cooperapplication Ser. No. 648,835, and in the following manner:

An aqueous slurry is prepared from 168 parts of 5-nitro-2-amino-anisolewith 1750 parts of water. To this is added a solution containing 108parts hydrochloric acid, 100%, and the slurry is stirred for tenminutes. This is then cooled to 0-5 C. by the addition of suflicientice, and this temperature is maintained throughout the diazotization.The volume is adjusted to 3500 parts with ice and water, anddiazotization is eflZected by the addition of 69 parts of sodiumnitrite, 100%, dissolved in 500 parts of water. Stirring is continuedfor an additional 30 minutes, at the end of which period the diazo isclarified. The clarified solution is a clear yellow color and ismaintained at 0-5 C. throughout coupling.

A solution of 68 parts of sodium hydroxide in 2500 parts of water isheated to C. To this is added gradually and with constant stirring 290parts of the ortho toluidide of beta-hydroxy naphthoic acid, andstirring is continued until solution is complete. The solution is thendiluted by the gradual addition of water to 5000 parts at 90 C., andthis is then added to a solution containing 5.6 parts of sodiumhydroxide and 53.5 parts of sodium carbonate diluted with water to22,500 parts at 30 C. The volume is adjusted to 30,000 parts at 30 C.prior to coupling.

Coupling is effected by adding the diazo at 0-5 C. to the orthotoluidide of beta-hydroxy naphthoic acid solution at 30 C. in 15minutes. Stirring is continued for 60 minutes, at the end of which timethe pH of the slurry is 951-05. The slurry is then heated to the boil in30 minutes, and maintained at this temperature for 15 minutes. The hotslurry is filtered immediately, and the press cake washed free ofsoluble chloride ion. The resulting maroon pigment is dried at 60 C. Theyield of dry pigment is 425 parts.

As a result of such admixture, .there was obtained my novel pigmentcomposition of special utility in synthetic resin enamels EXAMPLE II Analkyd resin enamel of the following composition was prepared, thedesignated pigment The pigment was ground in a ball mill with a portionof the resin solution and solvents, and the remaining ingredients weremixed with the resulting mill base at a later stage. The resultingenamel was of desired maroon shade and .of ex- Viscosity measurementswere made on a Krebs modification of the Stormer viscosimeter withpaddle type agitator, as described on page 308 of the 1946 edition ofGardner's treatise on "Physical and Chemical Examination of Paints.varnishes, Lacquers and Colors." Viscosities were recorded in KU (Krebsunits) as defined therein, the numerical values being a direct functionof the time required for the rotation of the paddle in the enamel. Thistesting method is also described in ASTM method D-562-44 except that thenumerical values are a different function of the time measured.

Using this test, the initial viscosity of the enamel of this example was65 KU and, on storage of the enamel for 8 days at 50 C., only a slightincrease to 68 KU was found to exist.

EXAMPLE III Enamels were made by the process of Example II, except thatinstead of employing therein the mixed pigment product resulting fromExample I, the separate pigments of such mixture were eitherindependently utilized or varying amounts thereof were employed as setforth in the followingtable, which table also lists their viscositiesafter various storage periods:

' Table I It is apparent from the above table that employment alone inthese enamels of either pigment used in my novel pigment compositionresults in enamels having initially usable viscosity but that suchviscosity disadvantageously increases substantially on aging. thereto,enamels containing the pigment mixture of this invention exhibit equalor lower initial In contrast vlscosities and desired resistance toviscosity in crease on aging.

The conditions of preparing the organic toners of said Copperapplication Ser. No. 648,835 and of coupling diazotized 5-nitro-2-aminoanisole with 2-hydroxy-3-naphthoic acid are obviously not criticalexcept for the requirement that the couplin bath be maintained in analkaline condition, as is readily apparent to anyone skilled in the artof azo pigments. To obtain the optimum results, it is preferred, in theinstance of the adjuvant pigment, that the alkalinity be maintained withsodium carbonate or bicarbonate, as shown above.

Similarly, although the manganese salt comprises a preferred form of thestabilizing pigment to be employed herein, because manganese as thesalt-forming metal promotes excellent durability in the pigment, saltsof other metals, such,

as those of calcium, barium, strontium, iron, nickel and cobalt, etc.,which are adapted to afford satisfactory insolubility characteristics inthe pigment can also be used. Likewise, the time and temperatureemployed in the metallization is variable, temperatures ranging from50-'100 C. being usually adequate. However, for purposes of controllingreactivity as described above, the cation appears to be relativelyunimportant. Both the free acid and the sodium salt have provedeffective but their tendency to solubility in many media renders suchforms less preferred and desirable.

The following comprises a structural formula of the stabilizing adjuvantpigment utilizable herein OH COOK in which X is one of the groupconsisting of hydrogen, the alkali metals, the alkaline earth metals,manganese, iron, nickel and cobalt. As noted, the particular salt of themetal used for conversion of the azo dye to its metallic salt isunimportant, availability and solubility in water being the onlyimportant considerations.

The manganese salt of this adjuvant pigment is capable of existing intwo forms which difier markedly in color, crystal structure, as shown bycharacteristic X-ray difiraction patterns, and in their effectivenessfor the control of reactivity. The process described in Example I givesthe more effective and hence preferred form which is characterized by adark maroon color in full shade and a relatively weak, bluish red tint.

If, however, the heat development conditions are made more rigorous(either a longer time at the boil or a still longer time at a somewhatlower temperature) a transformation occurs to a much lighter red in fullshade and to a very much stronger and yellower tint. In fact, asuperficial examination would indicate this form to have far moredesirable pigment properties but, strangely, it is much less efiectivein controlling reactivity of enamels such as those of the example given.

The characteristic differences in color of these products is alsoapparent from spectrophotometric curves made on a General ElectricRecording Spectrophotometer, particularly those made from full shadeinks of the two colors in lithographic varnish and from tints of thesesame inks in lithographic varnish, mixed with an ink containing apigment grade of zinc oxide in such proportions that the final inkcontained 1 part of colored pigment for 50 parts of zinc oxide.

While the invention has been illustrated as applied to the preparationof a coating composition containing a pigment mixture contemplated inthis invention and utilizing a conventional alkyd resin as the vehicle,it is also applicable to the production of enamels utilizing anyoil-modified synthetic resins such as melamine or ureaformaldehydemodified drying oil alkyds, melamine or urea-formaldehyde non-oxidizingoil alkyds, and the like, as well as to the preparation ofnitrocellulose lacquers and of oil type paints. Such general types ofutilizable coating compositions are referred to in U. S. Reissue Patent21,247 and U. 8. Pat. 2,225,665. My novel pigment complex isoutstandingly useful in the production I 7 of stable, durable syntheticresin or enamel-coatings employable in automobile finishes, throughdispersion of the pigment in synthetic resin vehicles through thecustomary paint grinding procedure in a ball, roller, or other type ofconventional mechanical mill with suitable modification of the-millbase. Resinated coating compositions containing an alkyd resin arewell-known, and comprise certain types of polyhydric alcohol-polybasicacid resins, especially the so-called modified polyhydricalcohol-polybasic acid resins or resinous condensation products obtainedby reacting one or more polyhydric alcohols and one or more polybasicacids with one or more modifying in gredients, such as drying oils,semi-drying oils, synthetic drying oils, and monobasic acids, etc. Onenotable example thereof comprises the condensation products of glyceroland phthalic anhydride with linseed oil. These synthetic resin vehiclesor solutions are usually prepared by heating a mixture of theresin-producing ingredients, other than solvents, at temperatures abovethe melting point and until completion of the resinification. Theproperties of the resin can be modified as desired by varying theingredients and conditions of preparation. As already noted, specificmodified alkyd resins contemplated hereunder include melamine orurea-formaldehydemodified drying oil alkyds, melamine modifiednon-oxidizing and urea-formaldehyde-modified non-oxidizing oil alkydresins.

It will be understood that many widely diiferen variations in theinvention may be resorted to without departing form its underlyingspirit and scope and that it is not to be construed as limited to thespecific embodiments hereinabove set out, except as defined in theappended claims.

I claim as my invention:

1. A new insoluble azo maroon pigment composition consisting of anintimate mixture of from about 75-95 parts by weight of the azo dyestuflhaving the formula:

and from about 25-5 parts by weight of the insoluble azo pigment havingthe formula:

OCH: (i)H COOX ton.

ill

auoam together with from about 25-5 parts by weight of the insolublemanganese salt of the azo D 8- ment having the formula:

OCH; on 0001 3. A new maroon pigment composition consisting of anintimate mixture of about 90 parts by weight of the insoluble azo maroonpigment having the formula: CH:

together with about 10 parts by weight of the insoluble manganese saltof the azo pigment having the formula:

4. A durable synthetic alkyd resin coating composition containing as anessential pigmenting ingredient a mixture comprising from about -95parts by weight of the azo dyestufi having the formula and as aviscosity stabilizing adiuvant for said composition, from about 25-5parts by weight of the azo pigment having the formula 0cm 0H 000xwherein X is selected from the group consisting of hydrogen and aninsolubilizing salt-forming metal.

5. A durable synthetic alkyd resin coating composition containing as anessential pigmenting ingredient a mixture comprising from about andfrom, as a viscosity stabilizing adjuvant for said composition, about25-5 parts by weight of the azo pigment which is characterized by a darkmaroon color in full shade and a weak, bluish red tint having theformula OCH; OH 000 together with, as a viscosity stabilizing adjuvantfor said composition, about'10 parts by weight oi. the insolublemanganese salt of the azo pigment having the formula:

' OCH n! COOMu ALFRED ANTHONY BRIZZOLARA.

The fol file of this patent:

Number Number REFERENCES CITED lowing references are of record in theUNL'LE D STATES PATENTS Name Date Laska et a1. May 17, 1932 MorschelMar. 17, 1936 Hucks Feb. 27, 1940 Siegel Dec. 24, 1940 FOREIGN PATENTSCountry Date Great Britain of 1912 Great Britain May 8, 1924 GreatBritain Sept. 1, 1930

4. A DURABLE SYNTHETIC ALKYD RESIN COATING COMPOSITION CONTAINING AS ANESSENTIAL PIGMENTING INGREDIENT A MIXTURE COMPRISING FROM ABOUT 75-95PARTS BY WEIGHT OF THE AZO DYESTUFF HAVING THE FORMULA